| 1. |
- Bombarda, F., et al.
(författare)
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Runaway electron beam control
- 2019
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 1361-6587 .- 0741-3335. ; 61:1
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Edwards, N.V., et al.
(författare)
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Optical characterization of wide bandgap semiconductors
- 2000
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Ingår i: Thin Solid Films. - 0040-6090 .- 1879-2731. ; 364:1, s. 98-106
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Tidskriftsartikel (refereegranskat)abstract
- Our work primarily concerns the characterization of wide-gap III-V nitride semiconductors, nondestructively and at variable temperature, with spectroscopic ellipsometry (SE) and reflectometry in the spectral range from 1.5 to 6 eV. In the case of GaN, there are three main concerns associated with such data: (a) the quantification of the dispersion of the index of refraction with energy, (b) the removal of surface overlayers in real-time, and (c) the determination of the variation of valence bands with biaxial stress and the quantification of residual stress in thin films. The SE and reflectance capabilities provide (1) broadband spectra from 1.5 to 6 eV, which yield information about (a) below the bandgap and (b) above it, and (2) high resolution spectra (less than 1 meV at 3.4 eV) in the vicinity of the gap (3.3-3.6 eV), which enables (c). Here we will discuss issues concerning the relation of (c) to GaN material and growth parameters, though similar data for other wide bandgap materials will be discussed where relevant. Specifically, optimal heterostructure design for potential valence band engineering applications will be discussed in the context of trends in residual stress as a function of film thickness, growth temperature and substrate orientation for GaN/AlN/6H-SiC heterostructures. Standard heterostructures are mostly compressive for samples less than about 0.7 µm thick, are tensile up to about 2 µm and then abruptly become less tensile with stress values near 1 kbar thereafter. Additionally, these trends can be circumvented for moderately thick (approximately 2 µm) GaN layers (normally>2 kbar, tensile) by the introduction of a `buried interface' approach, namely, a strain mediating layer (SML) above the standard high-temperature AlN buffer layer designed to yield a range of compressive stresses from 0 to 2 kbar. The strain characteristics but also the growth rates of subsequently deposited nitride layers can be modulated by changing the growth parameters of the SML. This is achieved by in situ techniques during crystal growth without degrading the optical and structural properties of the deposited layer, as confirmed by XRD, SEM, PL, and AFM data taken on the overlying GaN layers. These results are interpreted in terms of coefficient of thermal expansion data for the layers and data concerning the planarization of GaN layers and growth behavior in non-(0001) directions.
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| 3. |
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| 4. |
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| 5. |
- Madsen, L.D., et al.
(författare)
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Assessment of MgO(1 0 0) and (1 1 1) substrate quality by X-ray diffraction
- 2000
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Ingår i: Journal of Crystal Growth. - 0022-0248 .- 1873-5002. ; 209:1, s. 91-101
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Tidskriftsartikel (refereegranskat)abstract
- MgO{1 1 1} and {1 0 0} crystals are widely used as substrates for thin film growth, in many different areas of research such as superconductors, and other oxide, metal and nitride films, multilayers and superlattices. Since the quality of the thin film can be strongly dependent on that of the substrate, the optimal film properties will only be fully conceived if the substrate is well characterized in advance. The goal of this work was to create a characterization method which was inexpensive, fast, efficient, and of course nondestructive, for assessing imperfect metal-oxide substrates. X-ray diffraction (XRD) was chosen because of its low cost, simplicity, nondestructiveness, and the fact that we have access to many different parameters using the same instrument. The miscut of the MgO crystals studied herein were characterized with a high resolution of 0.01°. The number of domains, their distribution and their size were characterized by ?-f maps and topography measurements. In this case, atomic force microscopy (AFM) was found to be more appropriate for assessing roughness than X-ray reflectivity measurements.
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| 6. |
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| 7. |
- McCaffrey, J.P., et al.
(författare)
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Surface damage formation during ion-beam thinning of samples for transmission electron microscopy
- 2001
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Ingår i: Ultramicroscopy. - 0304-3991 .- 1879-2723. ; 87:3, s. 97-104
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Tidskriftsartikel (refereegranskat)abstract
- All techniques employed in the preparation of samples for transmission electron microscopy (TEM) introduce or include artifacts that can degrade the images of the materials being studied. One significant cause of this image degradation is surface amorphization. The damaged top and bottom surface layers of TEM samples can obscure subtle detail, particularly at high magnification. Of the techniques typically used for TEM sample preparation of semiconducting materials, cleaving produces samples with the least surface amorphization, followed by low-angle ion milling, conventional ion milling, and focused ion beam (FIB) preparation. In this work, we present direct measurements of surface damage on silicon produced during TEM sample preparation utilizing these techniques. The thinnest damaged layer formed on a silicon surface was measured as 1.5nm thick, while an optimized FIB sample preparation process results in the formation of a 22nm thick damaged layer. Lattice images are obtainable from all samples. Copyright © 2001 Elsevier Science B.V.
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| 8. |
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| 9. |
- Robbie, K., et al.
(författare)
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Formation of Ni-graphite intercalation compounds on SiC
- 2001
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 64, s. 155401-15540111
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Tidskriftsartikel (refereegranskat)
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| 10. |
- Wahab, Qamar Ul, et al.
(författare)
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Power Schottky rectifiers and microwave transistors in 4H-SiC
- 2000
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Ingår i: <em>Proc. of the International Workshop on Semiconductor Devices</em>. - 9780819436016 - 0819436011 ; , s. 668-671
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Konferensbidrag (refereegranskat)abstract
- The physical simulation, fabrication and characterization of 4H-SiC power Schottky diodes and physical simulations of power microwave transistors an presented. A record blocking voltage of 3.85 kV was achieved for a Schottky diode with a 43 μm thick epilayer grown by chimney CVD. For hot-wall CVD grown layers a blocking voltage of 3.6 kV was obtained. Simulations of power MESFETs showed maximum drain currents above 300 mA/mm and a drain breakdown above 150 volt An RF analysis showed the cut-off and the maximum frequency of oscillation for a device with a gate length of 0.5 μm to be 13 and 45 GHz respectively. The maximum achievable gain was above 10 dB ep to 26 GFz.
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